Photographic antibronzing agents



Patented Feb. 2, 1954 PHOTOGRAPHIG AN TIBRONZIN G AGENTS Henry J.Schwalenstocker, Rochester, N. Y., assignor to E. I. du Pont de Nemoursand Company, Wilmington, Del., a corporation of Delaware No Drawing.Application January 26, 1951, Serial No. 208,058

This invention pertains to photographic materials and more particularlyto light-sensitive silver halide emulsions. Still more particularly itpertains to photographic silver halide emulsions which producephotographic silver images which do not degrade in color upon drying atelevated temperatures.

The practice of hot-drying or hot-ferrotyping of photographic printscauses a degradation of the silver image characterized by an undesirablechange in color. In the case of certain emulsions a loss in density alsooccurs. For instance, developed blue-black silver images usually degradeto a purplish or plum color and warm-tone images of basically browncolor degrade to a green or black image upon hot-drying. Many compoundshave been proposed for addition to photographic silver halide emulsionsto prevent or reduce the color degradation described above. While someof the known materials reduce color degradation they have a tageous. Inaddition, such compounds cause a degradation in the basic image color ofwarmtone emulsions.

An object of the present invention is to provide photographic emulsionsthat yield developed silver images which do not undergo serious colordegradation upon hot-drying. Another object is to provide such emulsionswhich are not desensitized by the adjuvants which prevent colordegradation. A further object is to provide a simple and yet effectiveway of reducing color degradation by the addition of available chemicalcompounds. Still further objects will be apparent from the followingdescription of the invention.

It has been found that the incorporation of saltsof mercaptoazoles withN-hydrocarbonsubstituted biguanides and especially N-arylsubstitutedbiguanides with photographic silver halide emulsions provide a highdegree of color stabilization of the emulsions without any undesirableeffect on the light-sensitive properties of the emulsions.

' The salts referred to above may be represented by the general formula:

NHR

wherein R. is hydrogen, or an alkyl or aryl group 9 Claims. (01. 95-7)strong desensitizing action which is disadvan- 2 I and R is an alkyl oraryl group Z constitutes the residue of a mercaptoazole. Thus, R and Rmay be methyl, ethyl, propyl, isopropyl, isobutyl, phenyl, tolyl,naphthyl, etc., and I-IS--Z may be a mercaptoazole. Among the usefulmercaptoazoles are Z-mercaptdbenzthiazole, 2- mercaptobenzoxazole, and5-mercaptotetrazole and their alkyl and aryl substituted derivatives, e.g., l-phenyl-S-mercaptotetrazole, l-a-naphthyl 5 mercaptotetrazole, 1 5naphthyl 5- mercaptotetrazole, 1 p diethylamino phenyl- 5mercaptotetrazole, 1 o methoxy phenyl- 5 mercaptotetrazole, 1 p chlorphenyl 5- mercaptotetrazole, 2,5 dimercapto 1,3,4 thiadiazole. 1 benzyl5 mercaptotetrazole, 1- cyclohexyl 5 mercaptotetrazole, 1 methyl- 5mercaptotetrazole and 1 ethyl 5 mercaptotetrazole. r

The mercaptoazole salts of the N-hydrocarhon-substituted biguanides canbe prepared by reacting the merca'ptoazole and the N-arylbiguanide insubstantially equimolecular proportions in water or a methanol orethanol solution and allowing the addition salts to crystallize.

Photographic silver images can be improved by the use of the novel saltsdescribed above by introducing them from an aqueous solution or anethanol or methanol solution into the lightsensitive emulsion at somestage in its preparation prior to coating or into a subcoating orovercoating colloid composition, e. g., gelatin. Alternatively, thecompounds may be incorporated in the photographic emulsion layer beforeor during development, e. g., by including them in the developingsolution. They are preferably added to the photographic emulsion priorto coating.

In general, the salts are used in an amount of 0.1 to 1.0% by weight ofthe silver in the emulsion. When used in a gelatin overcoating or adeveloper solution or an ethanol or aqueous treating solution for thedeveloped and fixed layer a similar or equivalent amount should be used.

The invention will be further illustrated but is not intended to belimited by the following examples.

EXAMPLE I One gram of phenylbiguanide mercaptobenzothiazole salt (A) wasdissolved in 40.0 ml. of ethanol and this solution was added to a silverhalide photographic emulsion composed of approximately AgBr and 40%AgCl. The solution was added to the fluid emulsion immediately i r to cn -in. u n ii s eryi betw e made from these coatings shows that whilecom.-

pound (A) causes an increase. warmth. of. basic image color, compound(13) causes a decrease in warmth of color. Gomparison of coatingsemploying equal quantities of the two ma: terials indicates thatcompound (A): is more effective than compound (B) in stabilizing imagecolor on hot drying. The effect on sensitivity of. the emulsion is notedin Table I.

Table I Print Ex-- tity. Ad uvant posure Re- Added 1 quired 2 8O 70 20075 400 S 80 75 200 130 400 140 G5 1 Expressed in milliliters of solutionper unit of emulsion.

l Expressed as relative time of exposure required to produce matchedprints from a. given negative. (Larger numbers indicate slower emulsionspeed.)

EXA V P H A gelatin solution to be used as a protective coatingwhich-results-in a final gelatin concentration of approximately 1 byweight was prepared in the usual manner. Quantities oi? phenylbiguanide1-phenyl-5 mercaptotetrazole salt (A) were added tothe gelatin solutionsuch that the final concentration of (A) in the gelatin solution rangedfrom 0650 13001200 gram per liter. The resulting solutions were appliedas a protective layer to a coating ofphotographic emulsion such as-thatdescribed in Example I. Controlcoatings were made in whichlsphenyl-o-mercaptotetrazole (B) was present in comparable quantitiesand in which noadjuvant was present.

Examination of normallyand hot-dried prints made from exposedphotographic papers using these coatings in: this case showed thatcoinpound B in all cases caused an undesirable loss in warmthof basicimage color while compound A on the other hand increased warmth. ofbasic imagecolor. Further it was demonstratedthat, while only 0050 gramof compound A per liter of gelatin solution provided satisfactory colorstability on hot drying, compound B did not provide this degree ofstability when used in concentrations as high as 0.200 grams per literof gelatin solution. The effect of these, materialson emulsionsensitivity is noted in Table II.

l Expressed. in grams of material per liter of overcoating 531R 11.

4 EXAMPLE III When photographic prints made from an exposed anddeveloped printing paper made from an emulsion of the type described inExample I were immersed in a water solution of phenylbiguanidemereaptobenzothiazole salt of 0.0005M concentration for one minute afternormal processing it was found that color loss on hot drying wasmarkedly decreased as compared to prints which didnot receive suchtreatment.

EXAMPLE IV fine gram of o-tolylbiguanide l-phenyl-S-mercaptotetrazo'lesalt was dissolved in 400 ml. of ethanol and this solution was added toa silver halide photographic emulsion composed of approximately AgBr and40% AgCl. The solution was added to the emulsion immediately prior tocoating in quantitiesvarying between 200 and 800 ml, of solution perunit of emulsion.

Comparison of prints made from coatings of these emulsions with printsmade on coatings of similar emulsion containing no adjuvant shows thatthis material provides a distinct improvement in image color ofhot-dried prints.

EXAMPLE V Following the procedure of Example IV the following arylbiguanide salts were evaluated in the emulsion described in Example IV;

1. orTolylbiguanide mercaptobenzothiazole salt.

2. o-Tol'ylbiguanide mercaptobenzoxazole salt.

3. Phenylbiguanide 1 phenyl-5-mercaptotetrazole salt.

4. Phenylbiguanide mercaptobenzoxazole salt.

These compounds were all found to be effective in preventing loss ofcolor on hot-drying of prints and gave results comparable with thosedescribed in Example IV with the o-tolylguanide l-phenyl-SemercaptQtetraZole salt.

EXAMPLE VI I enumerated under Example V. Examination of the-above printsafter hot-drying as compared to untreated-prints shows that color lossis reduced in each case where prints were treated in a solution ofarylbiguanide salt.

EXAMPLE VII The following salts were prepared in ethanol such that thefinal concentration of solid salt in ethanol solution was of the orderof 1 gram per 40o ml; of solution:

(A) Phenyl biguanide 2,5 dimercapto 1,3,4-

thiadiazole (B)-Biphenyl biguanide 2,5 dimercapto 1,3,4-

thiadiazole (C) Biplrenyl biguanide-l-phenyl-5-mercaptotetrazole.

' thesesalts were found to yieldhot-dried prints with image colorsuperior to similar prints made from light-sensitive coatings made fromsimilar emulsions free from such respective adjuvants.

In place of the specific hydrocarbon-substituted biguanide mercaptoazolesalts described in the foregoing examples there may be substitutedequivalent amounts of other such salts which fall within the scope ofthe above general formula. Among the additional salts which give similarresults are: methyl, ethyl, phenyl and diphenyl biguanide 1-e-naphthyl-5-mercapto tetrazole or other substituted 5-mercaptotetrazole salts,5-mercapto 1,3,4-triazole salts, thio barbituric acid salts, salts ofmercapto thiodiazoles and mercapto pyrimidines. Orthotolylbiguanidesalts of the above mercapto compounds can also be used.

The compounds may be used in various types of emulsions which containsensitizing dyes and other agents, e. g., anti-fogging agents,colloidhardening agents, wetting and surface active agents,delusterants, etc. which modify the characteristics of an emulsion.

The invention is, of course, not limited to emulsions having gelatin asthe water-permeable colloid for the silver halide binding agent or theovercoating or subcoating. Suitable additional colloids includeagar-agar, polyglycuronic acids, zein, collodion, water-solublecellulose derivatives, such as substantially hydrolyzed celluloseacetate, cellulose esters of hydroxy monocarboxylic acids, e. g., lacticor glycolio acids, alkali metal salts of cellulose esters ofdicarboxylic acids, such as phthalic acid, polyvinyl alcohol, partiallyhydrolyzed polyvinyl acetate and interpolymers thereof with unsaturatedmaterials, such as styrene, maleic acid, etc., water-soluble polyvinylacetals and other hydrophilic synthetic or natural resins and polymericcompounds. Suitable hydrophilic colloids of the above types aredescribed in United States Patents 2,110,491, 2,276,322, 2,276,323,2,286,215 and 2,211,323.

An advantage of this invention is that it provides an effective way ofreducing the color degradation of photographic images when subjected tohot-drying. Another advantage is that the adjuvants do not have anysignificant desensitizing effect on the light-sensitivity of thephotographic emulsions. The use of phenylbiguanide2-mercaptobenzothiazole salt is especially advantageous in photographicwarm-tone paper emulsions. A further advantage is that the salts have ahigh degree of solubility in methanol, ethanol and water which meansthat they can readily be associated with emulsions and photographiclayers without the necessity of using expensive solvents and specialprocedures for their introduction into the photographic element. A stillfurther advantage is that the adjuvants can be readily prepared fromavailable chemicals.

As many widely different embodiments of this invention can be madewithout departing from the spirit and scope thereof, it is to beunderstood that the invention is not to be limited except as defined bythe claims.

What is claimed is:

1. A photographic element comprising a support bearing a light-sensitivesilver halide emulsion layer which contains a salt of a mercaptoazolewith an N-hydrocarbon-substituted biguanide in an amount constituting0.1% to 1.0% by weight of the silver in said emulsion.

2. A photographic element comprising a support bearing a light-sensitivesilver halide emulsion layer which contains a salt of a mercaptoazolewith an N-aryl-substituted biguanide in an. amount constituting 0.1% to1.0% by weight of the silver in said emulsion.

3. A photographic element comprising a paper base having agelatino-silver-halide emulsion layer containing a salt of amercaptoazole with an N-hydrocarbon-substituted biguanide in anamount-constituting 0.1% to 1.0% by weight of the silver in saidemulsion.

4. A photographic element comprising a paper base having agelatino-silver-halide emulsion layer containing a salt of amercaptoazole with an N-aryl-substituted biguanide in an amountconstituting 0.1% to 1.0% by weight of the silver in said emulsion.

5. A photographic element comprising a paper base bearing a gelatinosilver halide emulsion layer which contains a mercaptobenzothiazole saltof phenylbiguanide in an amount constituting 0.1% to 1.0% by weight ofthe silver in said emulsion.

6. The process of improving the color of a photographic silver imagewhich comprises incorporating with the silver halide emulsion layer of aphotographic paper prior to the completion of hot-drying a salt of amercaptoazole with an N-hydrocarbon-substituted biguanide in an amountconstituting 0.1% to 1.0% by weight of the silver in said emulsion.

7. The process of improving the color of a photographic silver imagewhich comprises incorporating with the silver halide emulsion layer of aphotographic paper prior to the completion of hot-drying a salt of amercaptoazole with an N-aryl-substituted biguanide in an amountconstituting 0.1% to 1.0% by weightof the silver in said emulsion.

8. A photographic silver halide emulsion containing a salt of amercaptoazole with an N- hydrocarbon-substituted biguanide, in an amountconstituting 0.1% to 1.0% by weight of the silver in said emulsion.

9. A photographic silver halide emulsion containing a salt of amercaptoazole with an N- aryl-substituted biguanide, in an amountconstituting 0.1% to 1.0% by weight of the silver in said emulsion.

HENRY J. SCHWALENSTOCKER.

References Cited in the tile of this patent UNITED STATES PATENTS NumberName Date 1,725,934 Reitstotter Aug. 27, 1929 1,763,989 Sheppard et al'June 17, 1930 2,317,184 Dreyfuss Apr. 20, 1943 2,368,647 Dreyfuss Feb.6, 1945 FOREIGN PATENTS Number Country Date 524,556 Great Britain Aug.8, 1940 573,745 Great Britain Dec. 4, 1945

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT BEARING A LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER WHICH CONTAINS A SALT OF A MERCAPTOAZOLE WITH AN N-HYDROCARBON-SUBSTITUTED BIGUANIDE IN AN AMOUNT CONSTITUTING 0.1% TO 1.0% BY WEIGHT OF THE SILVER IN SAID EMULSION. 